In the prior art, the automotive suspension mechanism uses the vibration-isolating bush at a portion connecting the car body and the suspension with a view to attenuating and absorbing the shocks. This vibration-isolating bush is generally provided with a shaft member such as an inner cylinder, an outer cylinder arranged at a spacing outside of the shaft member, and a rubbery elastic member interposed between the shaft member and the outer cylinder to bind the two elastically.
As the suspension mechanism having the vibration-isolating bush of this kind, a multi-link type rear suspension mechanism, as shown in FIG. 15 and FIG. 16, is disclosed in the following Patent Document 1. This suspension mechanism is provided with: an axle 62 for supporting a wheel 60 rotatably; a pair of front and rear upper links 64 and 66 connected at their one-end portions 64a and 66a rockably to an axle 62 and connected at their other-end portions 64b and 66b rockably to a suspension member 68 acting as a body side member; a pair of front and rear lower links 70 and 72 connected at their one-end portions 70a and 72a rockably to the axle 62 and connected at their other-end portions 70b and 72b rockably to the suspension member 68; and a toe control link 74 connected at its one-end portion 74a rockably to the axle 62 and connected at its other-end portion 74b rockably to the suspension member 68. Here, letter F designates the front side of the car body, and letter H designates the width direction of the car body.
Moreover, the other-end portions 64b, 66b, 70b, 72b and 74b of the individual links 64, 66, 70, 72 and 74 and the suspension member 68 are connected through vibration-insulating bushes 76, 78, 80, 82 and 84, respectively, and the individual vibration-isolating bushes have their axes p1, p2, p3, p4 and p5 arranged to along the directions perpendicular to the longitudinal directions r1, r2, r3, r4 and r5 of the individual links.
In the multi-link type suspension mechanism thus far described, as shown in FIG. 16, the individual links 64, 66, 70, 72 and 74 are set at inclined positions in a top plan view. Specifically, the lower link 70 on the front side is set in a top plan view to the inclined position, at which the inner side of the body width direction H is positioned on the body front side F. The lower link 72 on the rear side is set in a top plan view to the inclined position, at which the outer side of the body width direction H is positioned on the body front side F. The toe control link 74 is set in a top plan view to the inclined position, at which the outer side of the body width direction H is positioned on the body front side F.
While the vehicle is running, therefore, forces of various directions are inputted to the vibration-isolating bushes 80, 82 and 84, which are coupled mainly to the lower links 70 and 72 and the toe control link 74. If the suspension mechanism is vertically displaced with respect to the car body, for example, not only the forces in a twisting direction N (as referred to FIG. 2) but also the forces in a prying direction Z (as referred to FIG. 1) are applied to the vibration-isolating bushes 80, 82 and 84. If the suspension mechanism is transversely displaced with respect to the car body, on the other hand, not only the forces in a transverse direction Y (as referred to FIG. 1) but also the forces in an axial direction X (as referred to FIG. 1) are applied to the vibration-isolating bushes 80, 82 and 84.
In order to improve the riding comfortableness and the steering stability in the vibration-isolating bush of this kind, therefore, it is desired to reduce the spring constants in the twisting direction and in the prying direction while enlarging the spring constants in the transverse direction and in the axial direction.
For this desire, there has been developed the so-called “vibration-isolating bush of a bulge type” (as referred to the following Patent Document 2), in which the inner cylinder is provided at its axially central portion with a bulging portion bulging in the transverse direction so as to reduce the spring constant in the prying direction while enlarging the spring constant in the transverse direction. In order to enhance the spring constant more in the transverse direction, moreover, there is disclosed in the following Patent Document 3 a vibration-isolating bush of the aforementioned bulge type, which is constituted to have an intermediate cylinder between an inner cylinder and an outer cylinder.
Patent Document 1: JP-A-2005-112258,
Patent Document 2: JP-A-09-100859, and
Patent Document 3: JP-A-09-100861.